Raducanu's loss to Ostapenko means the 2021 US Open champion misses out on her first final of a regular WTA Tour eventGreat Britain's Emma Raducanu is out of the Korea Open after retiring injured from her semi-final against top seed Jelena Ostapenko.
The 19-year-old took a medical timeout during the second set as she struggled with a left glute injury.
She carried on as Ostapenko claimed the second set but conceded the match to the Latvian at 4-6 6-3 3-0.
Ostapenko will face second seed Ekaterina Alexandrova of Russia, who beat Germany's Tatjana Maria 6-2 6-4.
British number one Raducanu, who was playing in her first semi-final of a regular WTA Tour event, has struggled with various injuries and has retired mid-match on a number of occasions since winning the US Open in 2021.
After a nervy first service game where she was broken by the former French Open champion, Raducanu regained composure to break back immediately and claim a decisive break at 4-4 and then served out the set.
However, Ostapenko, who had edged ahead in the second set before Raducanu took her off-court medical timeout, took control of the match when the Briton returned to court but continued to grimace in pain.
After securing the second set 6-3, the 25-year-old raced 3-0 ahead in the third when Raducanu called it a day.
Raducanu had beaten Polish third seed Magda Linette in the quarter-finals to claim three wins in a row for the first time since her US Open victory last year.
